Gas turbine combustors and method of operation

ABSTRACT

New combustors, and methods of operating same, which produce lower emissions, particularly lower emissions of nitrogen oxides. Methods and means are provided for supplying separate streams of air to primary and secondary combustion zones of a combustor, for removing heat from said primary combustion zone, and reintroducing said heat into the combustor at a region spaced apart and downstream from said primary and secondary combustion zones.

United States Patent Quigg et al.

[451 Oct. 28, 1975 GAS TURBINE COMBUSTORS AND METHOD OF OPERATION Inventors: Harold T. Quigg; Robert M.

Schirmer, both of Bartlesville, Okla.

Phillips Petroleum Company, Bartlesville, Okla.

Filed: Apr. 11, 1974 Appl. No.: 460,018

Related U.S. Application Data Division of Ser. No. 238,317, March 27, 1972, Pat. No. 3,826,077, which is a continuation-in-part of Ser. No. 208,102, Dec. 15, 1971, abandoned.

Assignee:

U.S. Cl. 431/10; 60/3906; 60/3965;

431/352 Int. Cl. F02C 7/26 Field of Search 431/351, 352, 10; 60/3906, 39.74, 39.65, 39.69, 39.02; 432/222 [56] References Cited UNITED STATES PATENTS 3,368,604 2/1968 Mutchler 431/352 X 3,463,467 8/1969 Nesbitt 431/352 X 3,572,031 3/1971 Szetela.... 431/352 X 3,608,309 9/1971 Hill et al. 60/3965 FOREIGN PATENTS OR APPLICATIONS 691,876 5/1953 United Kingdom 431/352 Primary Examiner-Edward G. Favors [57] ABSTRACT New combustors, and methods of operating same,

which produce lower emissions, particularly lower 28 Claims, 17 Drawing Figures ii 11/ I IIIIIIII (3 car FUEL I US. Patent Oct. 28, 1975 Sheet 1 of 7 3,915,619

T M 2 2 on 2 mm $4 I US. Patent Oct. 28, 1975 Sheet 2 of7 3,915,619

US. Patent was, 1975 Sheet3of7 3,915,619

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US. Patent Oct. 28, 1975 Sheet4 0f7 3,915,619

U.S. Patent Oct.28,19 '75 Sheet60f7 3,915,619

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US. Patent Oct.28, 1975 Sheet7of7 3 ,915,619

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GAS TURBINE COMBUSTORS AND METHOD OF OPERATION This application is a division of copending application Ser. No. 238,317, filed Mar. 27, 1972, now US. Pat. No. 3,826,077 issued July 30, 1974, which was a continuation-in-part of then copending application Ser. No. 208,102, filed Dec. 15, 1971, now abandoned.

This invention relates to improved combustors and methods of operating same.

Air pollution has become a major problem in the United States and other highly industrialized countries of the world. Consequently, the control and/or reduction of said pollution has become the object of major research and development effort by both governmental and nongovernmental agencies. Combustion of fossil fuel is a primary source of said pollution. It has been alleged, and there is supporting evidence, that automobiles employing conventional piston-type engines buming hydrocarbon fuels are a major contributor to said pollution. Vehicle emission standards have been set by the United States Environmental Protection Agency which are sufficiently restrictive to cause automobile manufacturers to consider employing alternative en gines instead of the conventional piston engine.

The gas turbine engine is being given serious consideration as an alternate engine. However, insofar as we presently know, there is no published information disclosing realistic and/or practical combustors which can be operated at conditions typical of those existing in high performance engines, and which will have emission levels meeting or reasonably approaching thestandards set by said United States Environmental Protection Agency. This is particularly true with respect to nitrogen oxides emissions.

Thus, there is a need for a combustor of practical and/or realistic design which can be operated in a manner such that the emissions therefrom will meet said standards. Even a combustor giving reduced emission approaching said standards would be a great advance in the art. Such a combustor would have great potential value because it is possible the presently very restrictive standards may be reduced.

The present invention solves the above-described problems by providing improved combustors, and methods of operating same, which produce emissions meeting or reasonably approaching the present stringent standards established by said environmental protection agencies. Said methods comprise preferably supplying separate streams of air to primary and secondary combustion zones of a combustor, removing heat from said primary combustion zone, and reintroducing said heat into the combustor at a region spaced apart from and downstream from said primary and secondary zones.

Thus, according to the invention, there is provided a combustor comprising, in combination: a flame tube; air inlet means for introducing a first stream of air into the upstream end portion of said flame tube; fuel inlet means for introducing a fuel into the upstream end portion of said flame tube; at least one opening provided in the wall of said flame tube at a first station located intermediate the upstream and downstream ends thereof; a first conduit means communicating with said opening at said first station for maintaining a second stream of air separate from said first stream of air and admitting said second stream of air into the interior of said flame tube; at least one other opening provided in the wall of said flame tube at a second station located downstream from said first station; and a second conduit means surrounding said flame tube and communicating with said opening at said second station for maintaining a third stream of air separate from said first and second streams of air and flowing said third stream of air in a downstream direction over and in heat exchange with the outer wall of said flame tube so as to remove heat from the interior of said flame tube and heat said third stream of air and then admit same into the interior of said flame tube.

Further, according to the invention, there is provided a method for burning a fuel in a combustor, which method comprises: establishing separate streams of air as a first stream of air, a second stream of air, and a third stream of air; introducing said first stream of air initially into a swirl zone at the upstream end of a primary combustion zone of said combustor; exiting said first stream of air from said swirl zone into said primary combustion zone as a swirling stream of air; introducing a fuel into the upstream end of said swirl zone axially of said swirling stream of air so as to effect controlled mixing of said fuel and said air at the interface therebetween; expanding said swirling stream of air and said fuel in a uniform and graduated manner, during at least a portion of said mixing thereof, from the volume in the region of the initial contact therebetween to the volume of said primary combustion zone; burning said fuel; introducing said second stream of air, maintained separate from said first stream of air, into a secondary combustion zone of said combustor located downstream from said primary combustion zone; flowing said third stream of air, maintained separate from said first and second streams of air, in a downstream direction over and in heat exchange with an outer wall of said primary combustion zone so as to remove heat from the interior of said primary combustion zone and heat said air; and introducing said thus heated third stream of air into a third zone of said combustor located downstream from said secondary zone.

FIG. 1 is a view, partially in cross section, of a combustor in accordance with the invention.

FIGS. 2, 3, and 4 are cross section views taken along the line 2--2, 3-3, and 44, respectively, of FIG. 1.

FIG. 5 is a fragmentary perspective view of a combustor flame tube illustrating another type of fin or extended surface which can be employed thereon.

FIG. 6 is a cross section view taken along the line 66 of FIG. 1.

FIG. 7 is a partial view in cross section of another combustor in accordance with the invention.

FIG. 8 is a view in cross section taken along the line 88 of FIG. 7.

FIG. 9 is a partial view in cross section of another combustor in accordance with the invention.

FIGS. 10 and 11 are cross section views taken along the lines 10-10 and lll1, respectively, of FIG. 9.

FIG. 12 is a view in cross section of another type of dome or closure member whichcan be employed in the combustors of the invention.

FIGS. 13 and 14 are diagrammatic views, partially in cross section, of other combustors in accordance with the invention.

FIG. 15 is a partial view in cross section of another combustor in accordance with the invention.

FIG. 16 is a front elevation view taken along the line 1616 of FIG. 15.

FIG. 17 is a cross-sectional elevation view of the swirl plate of the dome or closure member in the combustor of FIG. 15.

Referring now to the drawings, wherein like reference numerals are employed to denote like elements, the invention will be more fully explained. In FIG. 1 there is illustrated a combustor in accordance with the invention, denoted generally by the reference numeral 10, which comprises an elongated flame tube 12. Said flame tube 12 is open at its downstream end, as shown for communication with a conduit leading to a turbine or other utilization of the combustion gases. A closure or dome member, designated generally by the reference numeral 14, is provided for closing the upstream end of said flame tube, except for the openings in said dome member. An outer housing or casing 16 is disposed concentrically around said flame tube 12 and spaced apart therefrom to form a first annular chamber 18 around said flame tube and said dome or closure member 14. Said annular chamber 18 is closed at its downstream end by any suitable means such as that illustrated. Suitable flange members, as illustrated, are provided at the downstream end of said flame tube 12 and outer housing 16 for mounting same and connecting same to a conduit leading to a turbine or other utilization of the combustion gases from the combustor. Similarly, suitable flange members and 17 are provided at the upstream end of said flame tube 12 and said outer housing 16 for mounting same and connecting same to a suitable conduit means which leads from a compressor or other source of air. As illustrated in the drawing, said upstream flange members comprise a portion of said outer housing or casing 16 which encloses dome member 14 and forms the upstream end portion of said first annular chamber 18. It will be understood that outer housing or casing 16 can be extended, if desired, to enclose dome 14 and said upstream flanges then relocated on the upstream end thereof. While not shown in the drawing, it will be understood that suitable support members are employed for supporting said flame tube 12 and said closure member 14 in the outer housing 16 and said flange members. Said supporting members have been omitted so as to simplify the drawing.

An air inlet means is provided for introducing a swirling mass or stream of air into the upstream end portion of flame tube 12. As illustrated in FIGS. 1 and 4, said air inlet means comprises a generally cylindrical swirl chamber 22 formed in said dome member 14. The downstream end of swirl chamber 22 is in open communication with the upstream end of flame tube 12. A plurality of air conduits 24 extend from said first annular chamber 18, or other suitable source of air, into swirl chamber 22 tangentially with respect to the inner wall thereof.

A fuel inlet means is provided for introducing a stream of fuel into the upstream end portion of flame tube 12. As illustrated in FIG. 1, said fuel inlet means comprises a hollow conduit 26 for introducing a stream of fuel into the upstream end of swirl chamber 22 and axially with respect to said swirling stream. of air. Any other suitable fuel inlet means can be employed.

A flared expansion passageway 28 is formed in the downstream end portion of dome or closure member 14. Said flared passageway flares outwardly from the downstream end of swirl chamber 22 to a point on the inner wall of flame tube 12.

An imperforate sleeve 30 surrounds an upstream portion of said flame tube 12. The outer wall of said sleeve 30 can be insulated if desired and thus increase its effectiveness as a heat shield. Said sleeve 30 is spaced apart from flame tube 12 so as to longitudinally enclose an upstream portion 18 of said first annular chamber 18 and define a second annular chamber 19 between said sleeve 30 and outer casing 16. An annular wall member 32, secured to the inner periphery of casing 16, is provided for closing the downstream end of said second annular chamber 19. At least one opening 34 is provided in the wall of flame tube 12 at a first station located intermediate the ends of said flame tube. In most instances, it will be preferred to provide a plurality of openings 34, as illustrated. A generally tubular conduit means 36 extends from said second annular chamber 19 into communication with said opening 34 for admitting a second stream of air from said second annular chamber 19 into the interior of flame tube 12. When a plurality of openings 34 are provided, a plurality of said tubular conduits 36 are also provided, with each individual conduit 36 being individually connected to an individual opening 34. The abovedescribed structure thus provides an imperforate conduit means comprising second annular chamber 19 and tubular conduit(s) 36 for admitting a second stream of air into the interior of flame tube 12.

At least one other opening 38 is provided in the wall of flame tube 12 at a second station located downstream and spaced apart from said first station for admitting a third stream of air from first annular chamber 18 into the interior of flame tube 12. In most instances, it will be preferred to provide a plurality of openings 38 spaced around the periphery of said flame tube, similarly as illustrated.

Preferably, the outer wall surface of flame tube 12 is provided with an extended surface in the form of fins or tabs mounted thereon in the region surrounded by sleeve 30, and which extend into the portion 18' of said first annular chamber which is enclosed by said sleeve. As illustrated in FIGS. 1, 2, and 3 said fins or tabs 40 and 42 can be arranged in rows which extend around the periphery of the flame tube 12, and which are spaced apart longitudinally on said flame tube. The fins or tabs 40, in each row thereof, can be spaced apart circumferentially to provide passageways 41 therebetween. See FIG. 2. Similarly, passageways 43 can be provided between the circumferentially spaced apart fins or tabs 42. See FIG. 3. FIG. 5 illustrates another type of fin which can be employed. In FIG. 5 the fins 44 extend longitudinally of flame tube 12. Said fins 40, 42, and 44 can extend into enclosed portion 18' any desired distance.

FIG. 6 illustrates one type of structure which can be employed to provide tubular conduits 36. A plurality of boss members 37, spaced apart circumferentially in a row around the periphery of flame tube 12, is provided downstream from the last row of fins 42. Said boss members 37 have the general shape of fins 40 and 42 and passageways 45 are provided therebetween, simi larly as for passageways 41 and 43 in the rows of fins 40 and 42. Said imperforate sleeve 30 extends over boss members 37, similarly as for fins 40 and 42, and said conduits 36 can be formed by cutting through said sleeve 30 and said boss members 37 into communication with openings 34 in flame tube 12. Said passageways 41, 43, and 45 thus provide communication from the upstream end of first annular chamber 18, through enclosed portion 18', around tubular conduits 36, and into the downstream portion of first annular chamber 18.

Referring now to FIG. 7, there is illustrated the 1 stream portion of another combustor in accordance with the invention. The downstream portion not shown is like the combustor of FIG. 1. In FIG. 7, a closure or dome member, designated generally by the reference numeral 46, is provided for closing the upstream end of flame tube 12, except for the openings in said dome member. Said dome member can be fabricated inte grally, i.e., as one element. However, in most instances it will be preferred to fabricate said closure member 46 as two or more elements, e.g., an upstream. element 48 and a downstream element 50. A generally cylindrical swirl chamber 52 is formed in said upstream element 48 of closure member 46. The downstream end of said swirl chamber 52 is in open communication with the upstream end of said flame tube 12. An air inlet means is provided for introducing a swirling mass of air into the upstream end portion of said swirl chamber 52 and then into the upstream end of said flame tube. As illustrated in FIGS. 7 and 8, said air inlet means comprises a plurality of air conduits 54 extending into said swirl chamber 52 tangentially with respect to the inner wall thereof. Said conduits 54 extend from first annular passageway or chamber 18 into said swirl chamber 52.

A fuel inlet means is provided for introducing a stream of fuel in a direction which is from tangent to less than perpendicular, but nonparallel, to the periphery of said stream of air. As illustrated in FIGS. 7 and 8, said fuel inlet means comprises a fuel conduit 56 leading from a source of fuel, communicating with a passageway 58, which in turn communicates with fuel passageway 60 which is formed by an inner wall of said dovmstream element 50 of closure member 46 and the downstream end wall of said upstream element 48 of closure member 46. It will be noted that the inner wall of .said downstream element is spaced apart from and is complementary in shape to the downstream end wall of said upstream element 48. The direction of the exit portion of said fuel passageway 60 can be varied over a range which is intermediate or between tangent and perpendicular, but nonparallel, to the periphery of the stream of air exiting from swirl chamber 52. Varying the direction of the exit portion of fuel passageway 60 provides one means or method for controlling the degree of mixing between the fuel stream and said air stream at the interface therebetween. As illustrated in FIG. 7, the direction of the exit portion of fuel passageway 60 is at an angle of approximately 45 with respect to the periphery of the air exiting from swirl chamber 52. As mentioned above, the direction of said exit portion can vary from between tangent and perpendicular,

.but nonparallel, to the periphery of the stream of air rally downstream direction. However, it is within the scope of the invention to introduce said fuel in an upstream direction. Shim 62 provides means for varying the width of said fuel passageway 60. Any other suitable means, such as threads provided on the wall of upstream element 48 and downstream element 50, can be provided for varying the width of said fuel passageway 60. As will be understood by those skilled in the art in view of this disclosure, the shape of the upstream inner wall of said downstream element 50 and the shape of the downstream end wall of said upstream element 48 can be changed, but maintained complementary with respect to each other, so as to accommodate the abovedescribed changes in direction and width of said fuel passageway 60.

Referring now to FIG. 9, there is illustrated the upstream portion of another combustor in accordance with the invention. The downstream portion of the combustor of FIG. 9 is like the combustor of FIG. 1. A closure member 64 is mounted in the upstream end of flame tube 12 in any suitable manner so as to close the upstream end of said flame tube except for the openings provided in said closure member. A generally cylindrical swirl chamber 66 is formed in said closure member 64. The downstream end of said swirl chamber is in open communication with the upstream end of said flame tube. An air inlet means is provided for introducing a swirling mass of air into the upstream end portion of said swirl chamber 66 and then into the upstream end of said flame tube 12. As illustrated in FIGS. 9 and 10, said air inlet means comprises a plurality of air conduits 68 extending into said swirl chamber 66 tangentially with respect to the inner wall thereof. Said conduits extend from annular space 74, similarly as in FIG. 1. The fuel inlet means in the combustor of FIG. 9 comprises a fuel supply conduit 70 which is in communication with three fuel passageways 72, which communicate with annular passageway 74, which in turn is in communication with a plurality of fuel conduits 76 extending tangentially through the downstream end portion of said closure member 64 and into a recess 78 formed in the downstream end portion of said closure member, and tangentially with respect to the inner wall of said recess. As illustrated in FIGS. 9 and 10, said air inlet conduits 68 are adapted to introduce air tangentially into swirl chamber 66 in.a clockwise direction (when looking downstream), and said fuel inlet conduits 76 in FIG. 11 are adapted to introduce fuel tangentially into said recess 78 in a counterclockwise direction. This is a presently preferred arrangement in one embodiment of the invention. However, it is within the scope of the invention to reverse the directions of said air inlet conduits 68 and said fuel inlet conduits 76, or to have the directions of both said air inlet conduits and said fuel inlet conduits the same, e.g., both clockwise or both counterclockwise.

Referring now to FIG. 12, there is illustrated another type of closure member or dome which can be employed with the flame tubes of the combustors described herein. In FIG. 12 closure member 78 is similar to closure member 64 of FIG. 9. The principal difference is that in closure member 78 a conduit means 80 is provided and extends through said closure member 78 into communication with. the upstream end portion of flame tube 12, for example. At least one swirl vane 82 is positioned in said conduit means 80 for imparting a swirling motion to the air passing through said conduit means 80. If desired, conduit means 80 can comprise an annular conduit, instead of the tubular conduit shown, with suitable swirl vanes installed therein.

,FIG. 13 is a diagrammatic illustration of a modification of the combustor of FIG. 1. In FIG. 13 a plurality of imperforate individual tubular openings 36' are each connected individually to individual openings 34' in the wall of flame tube 12. Said tubular conduits 36' extend longitudinally through annular chamber 18 to the upstream end thereof and are provided for admitting a second stream of air into the interior of said flame tube. Outer casing 16 and dome member 14 are essentially like their counterparts in FIG. 1. A third stream of air is admitted to the interior of flame tube 12 via said annular chamber 18' and openings 38'.

FIG. 14 is a diagrammatic illustration of another modification of the combustor of FIG. 1, which is similar to the combustor of FIG. 13. The principal difference is that in FIG. 14 the tubular conduits 36' extend transversely through annular chamber 18 and through outer casing 16 and then to the upstream end of the combustor.

Referring now to FIG. 15, there is illustrated the upstream portion of another combustor in accordance with the invention. The downstream portion of the combustor of FIG. is like the combustor of FIG. 1. A closure member or dome, designated generally by the reference numeral 85, is mounted in the upstream end of flame tube 12 so as to close the upstream end of said flame tube except for the openings provided in saidclosure member. Said closure member can be fabricated integrally, i.e., as one element. However, in most .instances it will be preferred to fabricate said closure member in a pluraltiy of pieces, e.g., an upstream element 86, a swirl plate 87 (see FIG. 17), and a downstream element or radiation shield 88. An air inlet means is provided for introducing a swirling mass of air into swirl chamber 89 which is formed between swirl plate 87 and radiation shield 88, and then into the upstream end of flame tube 12. As illustrated in FIGS. 15, l6, and 17, said air inlet means comprises a plurality of air conduits 90 and 90' extending through said upstream member 86 and said swirl plate 87, respectively. A plurality of angularly disposed baffles 91, one for each of said air conduits 90, are fonned on the downstream side of said swirl plate adjacent the outlets of said air conduits.

A fuel inlet means is provided for introducing a stream of fuel into the upstream end of flame tube 12. As illustrated in FIG. 15, said fuel inlet means comprises a fuel conduit 92 leading from a source of fuel, communicating with a passageway 93 formed in upstream element 86, which in turn communicates with chamber 94, also formed in element 86. A spray nozzle 95 is mounted in a suitable opening in the downstream side of said element 86 and is in communication with said chamber 94. Any other suitable type of spray nozzle and fuel inlet means can be employed, including other air assist atomization nozzles. For example, it is within the scope of the invention to employ other nozzle types for atomizing normally liquid fuels such as nozzles wherein a stream of air is passed through the nozzle along with the fuel.

It will be understood the combustors of the invention can be provided with any suitable type of ignition means and, if desired, means for introducing a pilot fuel to initiate burning.

In one method of operating the combustor of FIG. 1, a stream of air from a compressor (not shown) is passed, via a conduit connected to flange 17, into the upstream end of annular space 18. A first stream of air is passed from annular space 18, through tangential conduits 24, and into swirl chamber 22. Said tangential conduits impart a helical or swirling motion to the air entering said swirl chamber and exiting therefrom. This swirling motion creates a strong vortex action resulting in a reverse circulation of hot gases within flame tube 12. Said first stream of air comprises and can be referred to as primary air.

A stream of fuel, preferably prevaporized, is admitted, via conduit 26, axially of said swirling stream of air. Controlled mixing of said fuel and said air occurs at the interface therebetween. The fuel and air exit from swirl chamber 22 via expansion passageway 28 wherein they are expanded in a uniform and graduated manner, during at least a portion of the mixing thereof, from the volume in the region of the initial contact therebetween to the volume of the primary combustion zone, i.e., the upstream portion of flame tube 12.

A second stream of air, separate from said first stream of air, is passed from the upstream end of annular chamber 18 via second annular chamber 19, tubular conduits 36, and openings 34 into a second zone of the combustor which is located downstream from said primary combustion zone. Said second stream of air comprises and can be referred to as secondary air.

A third stream of air, separate from said first and second streams of air, is passed from the upstream end of annular chamber 18, via the enclosed portion 18, around tubular conduit 36, into the downstream portion of annular chamber 18, and then via openings 38 into a third zone of the combustor which is located downstream from said second zone. Said third stream of air comprises and can be referred to as quench air.

In the above method of operation, combustion of said fuel is initiated at least in said primary combustion zone with said first stream of air (primary air) and essentially completed, if necessary, in said second zone with said second stream of air. The resulting combustion gases are quenched in said third zone and the quenched gases exit the downstream end of the flame tube to a turbine or other utilization such as a furnace, boiler, etc. In the above method of operation, said third stream of air in flowing through enclosed portion 18' removes heat from the wall of the primary combustion zone thus lowering its temperature, thereby increasing the heat loss from the combustion gases, and thereby lowering the flame temperature within the primary combustion zone. Preferably, the outer wall of the primary combustion zone is provided with an extended surface, e.g., fins as shown in FIG. 1, so as to increase said heat removal from the primary combustion zone. A further advantage is realized in that said second stream of air flowing through annular chamber 19 is shielded from the hot wall of the combustor and is relatively cool. This also aids in reducing the flame temperature in the primary combustion zone. The air which is heated by heat loss from the combustor wall is used only in the quench zone of the combustor. This is a further aid in reducing said flame temperature by keeping said heated air out of the primary combustion zone; but the overall efficiency is maintained by the introduction of the heated air into said quench zone. As shown by the examples hereinafter, outstanding results have been obtained in reducing the emissions content of the com bustor gases, particularly with respect to decreasing the nitrogen oxides emissions.

In the above method of operation the relative volumes of said first, second, and third streams of air can be controlled by varying the sizes of the said openings, relative to each other, through which said streams of air are admitted to flame tube 12. Any other suitable method of controlling said air volumes can be em ployed. For example, flow meters or calibrated orifices can be employed in the conduits supplying said streams of air.

In one method of operating the combustor of FIG. 7, a stream of air from a compressor (not shown) is passed, via a conduit connected to flange 17, into annular space 18. A first stream of air is passed from annular space 18 through tangential conduits 54 into swirl chamber 52. Said tangential conduits 54 impart a helical or swirling motion to the air entering said swirl chamber and exiting therefrom. This swirling motion creates a strong vortex action resulting in a reverse circulation of hot gases within flame tube 12 upstream toward said swirl chamber 52 during operation of the combustor.

A stream of fuel, preferably prevaporized, is admitted via conduit 56, passageway 58, and fuel passageway 60. Fuel exiting from fuel passageway 60 is formed into an annular stratum around the swirling stream of air exiting from swirl chamber 52. This method of introducing fuel and air effects a controlled mixing of said fuel and air at the interface therebetween. Initial contact of said fuel and air occurs upon the exit of said air from said swirl chamber 52. Immediately after said initial contact the fuel and air streams (partially mixed at said interface) are expanded, in a uniform and graduated manner during passage of said fuel and air through the flared portion of member 50, from the volume thereof in the region of said initial contact to the volume of said combustion chamber and at a point in said flame tube downstream from said initial contact. Said expansion of fuel and air thus takes place during at least a portion of the mixing of said fuel and said air. The resulting mixture of fuel and air is burned and combustion gases exit the downstream end of flame tube 12. A second stream of air is admitted to the interiorof flame tube 12 from the upstream end of annular chamber 18 via second annular chamber 19, tubular conduits 36, and openings 34 as described above in connection with FIG. 1. A third stream of air is admitted to the interior of flame tube 12 via openings 38 as described above in connection with FIG. 1.

In one presently preferred method of operating the combustor of FIG. 9, the method of operation is similar to that described above for the combustors of FIGS. 1 and 7. A first stream of air is admitted to swirl chamber 66 via tangential inlet conduits 68 which impart a helical or swirling motion to said air. A stream of fuel, preferably prevaporized, is admitted via conduit 70, fuel passageways 72, and tangential fuel conduits 76 into recess 78 formed at the downstream end of said closure member 64. Said fuel is thus formed into an annular manner described above in connection with the combustors of FIGS. 1 and 7.

The method of operation of the combustors of FIGS. 13 and 14 can be substantially like that described above for the combustors of FIGS. 1, 7, and 9, taking into consideration the type of dome or closure member employed on the upstream end of flame tubes 12'. In the combustors of FIGS. 13 and 14 the second stream of air is admitted to flame tube 12' via tubular conduits 36. The third stream of air is admitted via openings 38'. In FIG. 14 said tubular conduits 36' can be connected to a common source of air (such as a header conduit) which also supplies the first and third streams of air, or said tubular conduits can be connected to a separate source of air. The combustor of FIG. 14 is particularly adapted to be employed in those embodiments of the invention wherein the stream of secondary air admitted through openings 34 can have a temperature greater than the temperature of the primary air admitted through dome or closure member 14'. When tubular conduits 36 are connected to the same source of air as in supplying chamber 18 the temperature of the secondary air can be substantially the same as, or can be increased to be greater than, the temperature of the primary air. Similarly, when conduits 36 are connected to a source of air other than that supplying chamber 18, the temperature of the secondary air can be substantially the same as, or greater than, the temperature of the primary air. Any suitable means can be employed for heating said secondary air, e.g., a separate heater or heat exchange means for heating the air passing through said conduits 36'.

In one preferred method, the operation of the combustor of FIG. 15 is similar to the above-described operation. of the combustor of FIG. 1, and reference is made thereto. The principal difference is in the operation of closure member 85 (FIG. 15) and closure memstratum around the swirling stream of air exiting from ber 14 (FIG. 1). In FIG. 15, primary air is passed through said openings and 90', strikes said baffles 91, and has a swirling motion imparted thereto in chamber 89. A swirling stream of air exits from swirl chamber 89 through the opening in radiation shield 88 which surrounds nozzle 95. A stream of liquid fuel is passed through conduit 92, passageway 93, chamber 94, and exits from nozzle in a generally cone-shaped discharge. Said fuel contacts sai-d stream of air, with said air stream assisting the action of nozzle 95 in atomizing said fuel.

The combustors of the invention wherein heat is removed from the combustion zone and reintroduced into the quench zone are particularly adapted to use fuels high in aromatic content. This is completely contra to conventional practice. The ASTM specification for Aviation Turbine Fuels (D 1655) limits the concentration of aromatics in both Jet A and Jet B turbine fuel to 20 percent maximum. Such fuels will have a hydrogen content in the range of about 13.5 to 14 weight percent. One reason for this limitation is to reduce flame radiance and loss of heat to the walls of the combustor. However, in the combustors of the invention this problem is solved by the above-described method of introducing three separate streams of air to the combustor. Thus, the use of high aromatic content fuels having high flame radiance is desirable and advantageous in the method of the invention in that nitrogen oxides emissions can be further reduced. Such fuel will have a hydrogen content of less than about 13.5 weight percent, preferably less than about 12 weight percent.

The following examples will serve to further illustrate the invention.

EXAMPLE I A series of test runs was made employing combustors in accordance with the invention and a typical standard or prior art combustor as a control combustor. The same fuel was used in all of said test runs. Properties of said fuel are set forth in Table I below. Design details of the combustors of the invention are set forth in Table II below. Said design details, e.g., dimensions, are given by way of illustration only and are not to be construed as limiting on the invention. Said dimensions can be varied within wide limits so long as the improved results of the invention are obtained. For example, the formation of nitrogen oxides in a combustion zone is an equilibrium reaction. Thus, in designing a combustion zone, attention should be given to the size thereof so as to avoid unduly increasing the residence time therein. It is desirable that said residence time not be long enough to permit the reactions involved in the forma tion of nitrogen oxides to attain equilibrium. In said Table II the combustors have been identified by a number which is the Same as the FIGURE number of the drawing in which they are illustrated. Combustor No. l was essentially as illustrated in FIG. 1. Combustor No. 1(a) was like combustor No. 1 except that the fins on the flame tube were modified by placing one-eighth inch bars longitudinally through each row of fins 40 and each row of fins 42. This provided a more linear path through enclosed area 18'. Combustor No. 1(b) was like combustor No. 1(a) except that the dome or closure member 14 was modified to use liquid atomized fuel and swirl vanes were employed to impart the helical swirl to the air admitted through said dome 14. Combustor No. 7(a) was like the combustor illustrated in FIG. 7 except that the fins on the flame tube were modified in the same manner as in combustors 1(a) and 1(b).

Said control combustor basically embodies the principal features of combustors employed in modern aircraft-turbine engines. It is a straight-through can-type combustor employing fuel atomization by a single simplex-type nozzle. The combustor liner was fabricated from 2-inch pipe, with added internal deflector skirts for air film cooling of surfaces exposed to the flame. Exhaust emissions from this combustor, when operated at comparable conditions for combustion, are in general agreement with measurements presently available from several different gas turbine engines. Said control combustor had dimensions generally comparable to the above-described combustors of the invention.

Each of said combustors of the invention and said control combustor was run at 12 test points or conditions, i.e., 12 different combinations of inlet-air temperature, combustor pressure, flow velocity, and heat 5 input rate. Test points or conditions 1 to 6 simulate idling conditions, and test points 7 to 12 simulate maximum power conditions. The combustors of the invention were run using a prevaporized fuel. The control combustor was run using an atomized fuel. In all runs the air stream to the combustors was preheated by conventional means. Analyses for content of nitrogen oxides (reported as NO), carbon monoxide, and hydrocarbons (reported as carbon) in the combustor exhaust gases were made at each test condition for each com- 15 bustor. Nitrogen oxides were determined by the Saltzman technique, Anal. Chem. 26, No. 12, 1954, pages 1949-1955. Carbon monoxide was measured by a chromatographic technique. Hydrocarbon was measured by the technique of Lee and Wimmer, SAE Paper 680679. Each pollutant measured is reported in terms of pounds per 1,000 pounds of fuel fed to the combustor. The results from test conditions 1 to 6 are set forth in Table III below. The results from test conditions 7 to 12 are set forth in Table IV below. The data set forth in Tables III and IV are mean values from duplicate runs at each test condition.

TABLE I PHYSICAL AND CHEMICAL PROPERTIES OF TEST FUEL Philjet ASO ASTM Distillation, F.

Initial Boiling Point 340 5 vol. evaporated 359 10 vol. evaporated 362 20 vol. evaporated 371 30 vol. evaporated 376 vol. evaporated 387 vol. evaporated 398 vol. evaporated 409 40 vol. evaporated 424 vol. evaporated 442 vol. evaporated 461 vol. evaporated 474 End Point 496 Residue, vol. 0.8 Loss, vol. 0.0

45 Gravity, degrees API 46.6

Density, lbs/gal. 6.615 Heat of Combustion, net, Btu/1b. 18,670 Hydrogen Content, wt. 14.2 Smoke Point, mm 27.2 Sulfur, wt. 0.001 Gum, mg/lOO ml 0.0

50 Composition, vol.

Paraffins 52.8 Cycloparaffins 34.5 Olefins 0.1 Aromatics 12.6 Formula (calculated) (Cu zz) Stoichiometric Fuel/Air Ratio, lb./lb. 0.0676

TABLE II COMBUSTOR DESIGN Combustor Number Variable l 1(a) 7(a) Closure Member Air Inlet Diameter, in. 0.875 0.875 0.875 0.625 Inlet Type Tangent Tangent Tangent Swirl Hole Diameter, in. 0.188 0.188 0.250 0.250 Number of Holes 6 6 6 6 Total Hole Area, Sq. in. 0.166 0.166 0.295 0.295 72 Total Combustor Hole Area 3.213 3.213 5.571 5.571 Fuel Slot, in. 0.005 Fuel Nozzle Type Simplex Spray Angle, deg. 45 Fuel Tube Diameter, in. 0.250 0.250

TABLE II Cntinued COMBUSTOR DESIGN Combustor Number Variable 1 1(8) Flame Tube 1st Station (34) Hole Diameter, in. /16 X 1* 5/16 X1 5/16 X1 5/16 X1 Total Number of Holes 8 8 8 8 Total Hole Area, sq. in. 2.500 2.500 2.500 2.500 7: Total Combustor Hole Area 48.393 48.393 47.214 47.214 2nd Station (38) Hole Diameter, in. 5/16 X1 5/16 1 5/16 X1 5/16 X1 Total Number of Holes 8 8 8 8 Total Hole Area. sq. in. 2.500 2.500 2.500 2.500 71 Total Combustor Hole Area 48.393 48.393 47.214 47.214 Combustor Cross Sect. Area, sq. in. 3.355 3.355 3.355 3.355 Total Combustor Hole Area, sq. in. 5.166 5.166 5.295 5.295 7: Cross-Sectional Area 153.933 153.933 157.777 157.777 Combustor Inside Diameter, in. 2.067 2.067 2.067 2.067 Primary Zone Length, in. 7.375 7.375 7.375 7375 Volume, cu. in. 24.748 24.748 24.748 24.748 Combustor Length, in. 18.437 18.437 18.437 18.437 Volume, cu. in. 61.867 61.867 61.867 61.867

*Holcs are 5/16" diameter at ends; slots are 1" long.

TABLE III COMPARISON OF EMISSIONS FROM COMBUSTORS AT IDLE CONDITIONS Test Conditions Combustor Operating Variables l 2 3 4 5 6 Temperature, Primary Inlet 900 900 900 900 900 900 Air, F. Pressure, in Hg. abs. 50 50 50 50 50 50 Velocity, Cold Flow, ft./sec. 250 250 250 400 400 400 Heat Input Rate, Btu/lb. Air 1 200 275 350 200 275 350 NITROGEN OXIDES lbs./ 1000 lbs. Fuel Combustors No.

Control Combustor C 3.4 3.4 3.2 2.2 2.1 2.3 Combustor 1(a) 1.8 1.2 2.2 1.6 1.2 1.7 Combustor 7(a) 2.0 1.4 2.4 1.4 1.4 1.6 Combustor 1(b) 1.2 1.3 1.0 1.0 0.7 1.4 Combustor 1 0.0 0.5 2.0 0.0 0.2 0.2

CARBON MONOXIDE lbs/1000 lbs. Fuel Combustors No.

Control Combustor C 10 2 0 l7 9 0 Combustor 1(a) 26.5 0 1.5 33.5 9 3 Combustor 7(a) l4 0 0 17 6 0 Combustor 1(b) 28 5.5 4.5 34 7 Combustor 1 2 0 O 6 1.5 O

HYDROCARBONS lbs./ 1000 lbs. Fuel Combustors N0.

Control Combustor C 0.6 0.7 0.4 0.9 0.4 0.8 Combustor 1(a) 0.2 0. l 0.0 0.2 0.1 0.0 Combustor 7(a) 0.2 0.2 0.1 0.2 0.2 0.1 Combustor 1(h) 1.0 1.6 0.2 0.6 0.6 0.7 Combustor 1 0.4 0.2 3 .5 0.2 0.1 5.6

TABLE IV COMPARISON OF EMISSIONS FROM COMBUSTORS AT MAXIMUM POWER CONDITIONS Test Conditions Combustor Operating Variables 7 8 9 l0 1 1 12 Temperature, Primary Inlet 1 l 100 1 100 1 100 l 100 1 100 Air, F.

Pressure, in. Hg. abs. 110 110 110 110 110 Velocity, Cold Flow, ft./sec. 250 250 250 400 400 400 Heat Input Rate, Btu/1b. Air 225 300 150 225 300 NITROGEN OXIDES lbs/1000 lbs. Fuel Combustors No.

Control Combustor C 10.7 1 1.2 10.0 9.9 8.0 7.4 Combustor 1(a) 2.9 2.6 3.0 2.6 2.2 2.4 Combustor 7(a) 14.5 2.6 2.8 19.4 2.3 2.5 Combustor 1(b) 1.4 2.0 2.5 2.0 1.8 2.2 Combustor 1 0.0 0.6 2.2 0.0 0.0 1.4

TABLE IV -Continued COMPARISON OF EMISSIONS FROM COMBUSTORS AT MAXIMUM POWER CONDITIONS Test Conditions Combustor Operating Variables 7 8 9 10 I I 12 CARBON MONOXIDE lbs/1000 lbs. Fuel Combustors No.

Control Combustor C 0 0 0 0 0 Combustor l (a) 0 5 l8 0 0 Combustor 7(a) 0 0 0 12.5 2.5 0 Combustor 1(b) 13.5 8 7 36 6.5 1.5 Combustor I 0 0 0 3 0 0 HYDROCARBONS lbs/1000 lbs. Fuel Combustors No.

Control Combustor C 0.2 0.1 0.2 0.2 0.2 0.2 Combustor 1(a) 0.2 0.1 0.1 0.2 0.2 0.1 Combustor 7(a) 0.2 0.2 0.1 0.2 0.2 0.1 Combustor 1(b) 0.5 0.2 0.2 0.4 0.2 0.2 Combustor 1 0.6 0.3 0.2 0.6 0.9 0.5

EXAMPLE ll Referring to the above Tables III and IV, the data there given clearly show that all the combustors of the invention gave results markedly superior to the results obtained with the control combustor. Combustor No. l, in particular, gave outstanding results at practically all test conditions with respect to nitrogen oxides emissions, the pollutant most difficult to control. Said data also show that all the combustors of the invention can be operated at idle conditions to give not more than about 2 pounds of nitrogen oxides emissions per 1,000 pounds 'of fuel burned, and not more than about 3.5 pounds of nitrogen oxides emissions per 1,000 pounds of fuel burned at maximum power conditions. Such operating conditions would be preferred operating conditions.

Another series of test runs was carried out employing combustors l and 1(b) of Example I. In these runs the heat input (fuel flow) was varied, with the air flow remaining fixed, at different combinations of combustor pressure, reference velocity, and inlet air temperature. Each of said combustors was operated at the test points or conditions set forth in Table V below. Combustor No. l was run using a prevaporized fuel. Combustor No. 1(b) was run using a liquid atomized fuel. Properties of the fuel used in both combustors are set forth in Table 1 above. Analyses for emissions content in the combustor exhaust gases were carried out as in Example I. The emissions data for said test runs are set .forth in Tables VI and VII below. The emissions data set forth in said Tables VI and VII are mean values from duplicate runs at each test condition.

TABLE V COMBUSTOR NOS. 1 & l(b) TEST CONDITIONS Primary Cold Flow Test Inlet Air Combustor Reference Condition Temperature, Pressure, Velocity, Heat Input. Air Flow, Fuel Flow,

Number F. in. Hg. abs. ftJsec. Btu/lb. Air lb./sec. lb./hr.

1 1100 110 250 0.545 7.9 2 11.6 3 15.8 4 19.4 5 225 23.6 6 260 27.3 7 300 31.5 8 900 110 250 75 0.625 9.0 9 H H H 110 H 133 10 150 18.1 11 185 22.3 12 H H H 225 H 13 260 31.3 14 .300 36.2 15 700 110 250 75 0.733 10.6 6 H H H 110 H 15.5 17 150 21.2 18 185 26.1 19 225 31.8 20 260 36.7 21 300 42.4 22 500 110 250 75 0.885 12.8 23 110 18.8 24 H H H 150 H 2513 25 185 31.6 26 225 38.4 27 260 44.4 28 H H H 300 H 5L2 TABLE V Continued COMBUSTOR NOS. 1 & 1(b) TEST CONDITIONS Primary Cold Flow Test lnlet Air Combustor Reference Condition Temperature, Pressure, Velocity, Heat Input, Air Flow, Fuel Flow,

Number F. in. Hg. abs. ft./sec. Btu/lb. Air lb./sec. lb./hr.

TABLE VI SUMMARY OF EM1SSION DATA FROM COMBUSTOR NO. 1

Test Primary Zone Condition Residence Equivalence Emissions, lbs./ 1000 lbs. fuel Number Time, msec Ratio, d NO (as NO) CO HC (as C) TABLE V11 SUMMARY OF EMISSION DATA FOR COMBUSTOR NO. 1(b) Test Primary Zone Condition Residence Equivalence Emissions, lbs./ 1000 lbs. fuel Number Time, msec Ratio, d) NO, (as NO) CO HC (as C) TABLE VII Continued SUMMARY OF EMISSION DATA FOR COMBUSTOR NO. 1(b) Test Primary Zone Condition Residence Equivalence Emissions, lbs/1000 lbs. fuel Number Time, msec Ratio, d: NO, (as NO) CO HC (as C) The data in the above Tables VI and VII show that decreasing the temperature of the inlet air to the primary combustion zone decreases the N0 emissions. The temperature of the inlet air to the second zone of the combustor (inlet at openings 34) was not measured but approximated the temperature of the primary air introduced through air inlet conduits 24. CO emissions decreased with an increase in temperature of the inlet air to the second zone of the combustor. Thus, as discussed further hereinafter, in some embodiments of the invention, it is preferred that the temperature of the secondary air admitted to the second zone of the combustor be greater than the temperature of the air admit ted to the primary combustion zone.

Said data also show that, generally speaking, increasing combustor pressure increases NO, emissions; but increasing reference velocity decreases NO, emissions. In general, NO, emissions decrease with increasing equivalence ratio in the primary combustion zone (increasing fuel-rich mixture), and tend to plateau at low levels with increase in heat input. Said equivalence ratios were calculated from the percent Total Combustor Hole Area for the air inlet conduits 24 to the primary combustion zone. See combustors l and 1(b) in Table II. In general, CO emissions tended to peak at intermediate levels of heat input, decreased with an increase in combustor pressure, and increased with an increase in reference velocity.

EXAMPLE III Another series of test runs was carried out employing combustor l of Example I and five modifications thereof, i.e., combustors 1(0), 1(d), l(e), l0), and 1(g). Referring to FIGS. 1 and 4, said five modified combustors were essentially like combustor 1 except for the diameter of air inlet conduits 24. Design details of said combustors are set forth in Table VI below. Design details of combustor l are set forth in Table II above. Said design details, e.g., dimensions, are given by way of illustration only and are not to be construed as limiting on the invention. Said dimensions can be varied within wide limits so long as the improved results of the invention are obtained.

Each of said combustors was run at 12 test points or conditions, i.e., 12 different combinations of inlet-air temperature, combustor pressure, flow velocity, and heat input rate, similarly as in Example I. Said combustors were run using the same fuel, prevaporized, as in Examples 1 and 11. Operating conditions are set forth in Table IX below. Analyses of the combustor exhaust gases were carried out as in Example I. The emissions data for said test runs are set forth in Table X below. Said data are mean values from duplicate runs at each test condition.

, TABLE VI Variable COMBUSTOR DESIGN Combustor Number Closiire Member Air lnlet diameter,in.

Inlet Type Hole Diameter, in. Number of holes Total Hole Area, sq. in. Total Comb. Hole Area Fuel Nozzle Type Spray Angle, deg. Fuel Tube Diameter TABLE VIII Continued COMBUSTOR DESIGN Combustor Number Variable l(c) l(d) l(e) l(f) Flame Tube 1st Station (34) Hole Diameter, in. /16 1 5/16 X1 5/16 X1 5/16 1 Number of holes 8 8 8 8 Total Hole Area, sq. in. 2.500 2.500 2.500 2.500 7c Total Comb. Hole Area 49.271 48.761 47.985 47.628 2nd Station (38) Hole Diameter, in. 5/16X1 5/16Xl 5ll6 1 5/16X1 Number of holes 8 8 8 8 Total Hole Area, sq. in. 2.500 2.500 2.500 2.500 7: Total Comb. Hole Area 49.271 48.761 47.985 47.628 Comb. Cross-Sect. Area, sq. in. 3.355 3.355 3.355 3.355 Total Comb. l-Iole Area, sq. in. 5.074 5.127 5.210 5.249 7c CrossSect. Area 151.119 152.771 155.244 156.406 Combustor Inside Diameter, in. 2.067 2.067 2.067 2.067 Primary Zone Length, in. 7.375 7.375 7.375 7.375 Volume, cu. in. 24.748 24.748 24.748 24.748 Combustor Length, in. 18.437 18.437 18.437 18.437 Volume. cu. in. 61.867 61.867 61.867 61.867

Hg) 01) l(i) (j) Closure Member Air Inlet diameter, in. 0.875 0.875 0.875 0.625 Inlet Type Tangent Tangent Tangent Swirl Hole Diameter, in. 0.250 0.188 0.250 0.250 Number of holes 6 6 6 6 Total Hole Area, sq. in. 0.295 0.166 0.295 0.295 92 Total Comb. Hole Area 5.571 3.213 5.571 5.571 Fuel Nozzle Type Simplex Spray Angle, deg. Fuel Tube Diameter 0.250 0.250 0.250 Flame Tube 1st Station (34) Hole Diameter, in. 5/16 X1 5/16 X1 5/16 l 5/16 X1 Number of holes 8 8 8 8 Total Hole Area, sq. in. 2.500 2.500 2.500 2.500 7: Total Comb. Hole Area 47.214 48.393 47.214 47.214 2nd Station (38) Hole Diameter, in. 5ll6 l 5/16 1 5/16 1 5/16 1 Number of holes 8 8 8 8 Total Hole Area, sq. in. 2.500 2.500 2.500 2.500 7: Total Comb. Hole Area 47.214 48.393 47.214 47.214 Comb. Cross-Sect. Area, sq. in. 3.355 3.355 3.355 3.355 Total Comb. Hole Area, sq. in. 5.295 5.166 5.295 5.295 7: Cross-Sect. Area 157.777 153.933 157.777 157.777 Combustor Inside Diameter, in. 2.067 2.067 2.067 2.067 Primary Zone Length. in. 7.375 7.375 7.375 7.375 Voluine, cu. in. 24.748 24.748 24.748 24.748 Combustor Length, in. 18.437 18.437 18.437 18.437 Volume, cu. in. 61.867 61.867 61.867 61.867

TABLE IX TEST CONDITIONS Combust0rs1,l(c), l(d),1(e),1(f), and Hg) Primary 1 Cold Flow Test Inlet Air Combustor Reference Condition Temperature, Pressure, Velocity, Heat Input, Air Flow. 1 Fuel Flow.

Number F. in. Hg. abs. ft./sec. Btu/lb. Air lbJsec. 1b./hr.

1 900 250 200 0.284 10.9 2 275 15.0 3 H I, H 350 I, 19.1 4 900 50 400 200 0.455 17.5 5 H I, I, 275 I, 241 6 H I, H 350 1, 3O] 7 1100 250 0.545 15.7 8 I, 1, H 225 I, 23.6 9 I, I, ,1 300 H 3 L5 10 1100 110 400 150 0.872 25.2 11 225 37.8 12 300 50.4

TABLE X SUMMARY OF EMISSION DATA FROM COMBUSTORS l, l(c), l(d), l(e), 1(f)& l(g) Combus Test Condition Number tor No. 1 2 3 4 5 6 7 8 9 1O 11 12 Nitrogen Oxides, lbs. NQ /IOOO lbs. Fuel (as NO) l(g) 2.2 0.8 2.1 1.2 1.3 1.4 9.8 2.5 1.8 13.0 2.2 2.0 l(f) 0.6 1.6 2.8 0.6 1.2 2.0 2.9 2.4 2.7 2.6 2.2 3.9 l(e) 0.9 1.6 3.2 1.4 1.2 1.8 2.0 2.3 2.9 2.4 1.7 3.4 1 1.2 1.6 2.0 0.8 1.2 1.6 2.4 2.8 3.4 2.5 2.4 3.3 l(d) 0.8 1.2 2.4 0.6 l 4 1.8 2.0 2.0 3.3 2.0 1.8 3.2 l(c) 2.3 2.4 3.1 2.0 1 8 2.2 2.8 3.6 6.0 2.5 2.9 4.8

TABLE X Continued SUMMARY OF EMISSION DATA FROM COMBUSTORS 1, l(c), l(d), l(e), 1(f)& l(g) Combus- Test Condition Number tor No. 1 2 3 4 5 6 7 8 9 10 11 12 Carbon Monoxide, lbs. CO/1000 lbs. Fuel Hg) 3 l 4 47 12 l 8 2 2 l2 l l(f) 32 7 8 28 14 6 8 0 0 12 l 0 He) 60 18 6 47 33 12 9 2 0 l7 2 0 1 56 26 8 50 38 14 7 2 2 16 4 0 l(d) 32 24 14 43 56 17 11 2 0 17 4 0 He) 48 24 20 77 76 12 2 0 13 l Hydrocarbons, lbs. HC/l000 lbs. Fuel (as C) l(g) 0.4 0.1 0.0 0.4 0.2 0.2 0.1 0.1 0.1 0.2 0.1 0.1 l(f) 0.2 0.1 0.1 0.2 0.1 0.0 0.2 0.1 0.1 0.2 0.1 0.1 l(e) 0.4 0.2 0.0 0.2 0.8 0.2 0.2 0.2 0.1 0.3 0.2 0.1 l 0.2 0.1 0.1 0.2 0.1 0.1 0.1 0.1 0.1 0.2 0.1 0.2 l(d) 0.2 0.2 0.0 0.3 0.3 0.0 0.2 0.5 0.1 0.2 0.1 0.1 He) 1.1 0.6 0.6 1.8 0.8 0.1 0.4 0.2 0.1 0.2 0.2 0.1

Residence Time. msec l(g) 44.1 44.1 44.1 27.5 27.5 27.5 44.2 44.2 44.2 27.6 27.6 27.6 l(f) 51.8 51.8 51.8 32.3 32.3 32.3 51.9 51.9 51.9 32.4 32.4 32.4 l(e) 61.0 61.0 61.0 38.1 38.1 38.1 61.0 61.0 61.0 38.2 38.2 38.2 1 76.5 76.5 76.5 47.7 47.7 47.7 76.6 76.6 76.6 47.8 47.8 47.8 l(d) 99.2 99.2 99.2 61.9 61.9 61.9 99.3 99.3 99.3 62.1 62.1 62.1 l(e) 168.6 168.6 168.6 105.2 105.2 105.2 168.7 168.7 168.7 105.5 105.5 105.5

Equivalence Ratio. d)

l(g) 2.83 3.89 4.96 2.84 3.90 4.98 2.12 3.19 4.26 2.13 3.19 4.26 l(f) 3.32 4.58 5.82 3.33 4.59 5.85 2.49 3.75 5.01 2.50 3.75 5.01 l(e) 3.92 5.38 6.85 3.92 5.40 6.88 2.93 4.42 5.89 2.95 4.42 5.89 1 4.91 6.75 8.60 4.91 6.78 8.65 3.68 5.54 7.40 3.70 5.54 7.40 l(d) 6.38 8.75 11.20 6.38 8.80 11.20 4.77 7.18 9.60 4.79 7.18 9.60 l(e) 10.80 14.94 18.96 10.88 14.94 18.96 8.13 12.22 16.25 8.13 12.22 16.25

EXAMPLE IV Another series of test runs was carried out employing three additional combustors l(h), l(i), and 1(1). Combustor l(h) was essentially like combustor 1 of Example I. Combustor l(i) was a modification of combustor 1 and was essentially like combustor l(g) of Example III. Combustor l( was a modification of combustor l and was essentially like combustor l(b) of Example I.

Design details of said combustors are set forth in Table VIII above. Said design details, e.g., dimensions, are given by way of illustration only and are not to be construed as limiting on the invention. Said dimensions can be varied within wide limits so long as the improved results of the invention are obtained.

Each of said combustors was run at 12 test points or conditions, i.e., 12 different combinations of inlet air temperature, combustor pressure, flow velocity, and heat input rate, similarly as in Example I. Saidcombustors were run using the same fuel as in the other examples. Combustors l(h) and l(i) were run using prevaporized fuel. Combustor l( was run using atomized liquid fuel. Operating conditions were the same as for the runs in Example 111 and are set forth in Table IX above. Analyses of the combustor exhaust were carried out as in the other examples. Emission data, mean values from duplicate runs at each test condition, are set forth in Table XI below.

TABLE XI SUMMARY OF EMISSION DATA FROM COMBUSTORS l(h), l(i), AND l(j) Emissions, lbs./ 1000 lbs. Fuel for Combustor Confg. Nos.

Test NO (as NO) CO l-IC (as C) Condition Combustor Number Combustor Number Combustor Number Number l(h) l(i) l(j) l(h) l(i) l(j) l(h) l(i) l(j) 

1. A combustor, comprising, in combination: a flame tube; air inlet means for introducing a first stream of air into the upstream end portion of said flame tube; fuel inlet means for introducing a fuel into the upstream end portion of said flame tube; at least one opening provided in the wall of said flame tube at a first station only which is located intermediate the upstream and downstream ends thereof; a first conduit means communicating with said opening at said first station for maintaining a second stream of air separate from said first stream of air and for admitting said second stream of air from said first conduit means into the interior of said flame tube at only said first station; at least one other opening provided in the wall of said flame tube at a second station only which is located downstream from said first station; and a second conduit means surrounding said flame tube and communicating with said openIng at said second station for maintaining a third stream of air separate from said first and second streams of air and for flowing said third stream of air in a downstream direction over and in direct heat exchange with the outer wall of said flame tube so as to remove heat from the interior of said flame tube and heat said third stream of air and then for admitting same into the interior of said flame tube at only said second station downstream from said first station.
 2. A combustor, comprising, in combination: an outer casing; a flame tube disposed within said casing and spaced apart therefrom to form a first annular chamber comprising a first annular air conduit means between said flame tube and said casing; an imperforate sleeve surrounding an upstream portion of said flame tube and spaced apart therefrom to longitudinally enclose an upstream portion of said first annular chamber and form a second annular chamber between said sleeve and said outer casing, with said second annular chamber comprising a second annular air conduit means surrounding the upstream portion of said first annular air conduit means; air inlet means for introducing a first stream of air into the upstream end portion of said flame tube; fuel inlet means for introducing a fuel into the upstream end portion of said flame tube; at least one opening provided in the wall of said flame tube at a first station located intermediate the upstream and downstream ends thereof and communicating with the downstream end portion of said second annular air conduit means for admitting a second stream of air, maintained separate from said first stream of air, into the interior of said flame tube; and at least one other opening provided in the wall of said flame tube at a second station located downstream from said first station and communicating with the downstream end portion of said first annular air conduit means for admitting a third stream of air, maintained separate from said first and second streams of air, into the interior of said flame tube.
 3. A combustor, comprising, in combination: an outer casing; a flame tube disposed within said casing and spaced apart therefrom to form a first annular chamber between said flame tube and said casing; air inlet means for introducing a first stream of air into the upstream end portion of said flame tube; fuel inlet means for introducing a fuel into the upstream end portion of said flame tube; at least one opening provided in the wall of said flame tube at a first station located intermediate the upstream and downstream ends thereof; an imperforate conduit means spaced from said flame tube but extending through said first annular chamber and communicating with said opening at said first station for admitting a second stream of air into the interior of said flame tube; and at least one other opening provided in the wall of said flame tube at a second station located downstream from said first station for admitting a third stream of air from said first annular chamber into the interior of said flame tube.
 4. A combustor according to claim 3 wherein: said opening provided in said flame tube at said first station comprises a plurality of openings spaced around the periphery of said flame tube; and said imperforate conduit means comprises a plurality of individual tubular conduits each connected individually to individual openings of said plurality of openings.
 5. A combustor according to claim 4 wherein each of said tubular conduits extends transversely through said first annular chamber and through said outer casing.
 6. A combustor according to claim 3 wherein said imperforate conduit means comprises: an imperforate sleeve surrounding an upstream portion of said flame tube and spaced apart therefrom to longitudinally enclose an upstream portion of said first annular chamber and form a second annular chamber between said sleeve and said outer casing; a baffle member secuRed to the inner wall of said casing and the downstream end of said sleeve for closing the downstream end of said second annular chamber; and a tubular conduit means extending from said second annular chamber into communication with said opening at said first station in the wall of said flame tube.
 7. A combustor according to claim 6 wherein: said opening provided in said flame tube at said first station comprises a plurality of openings spaced around the periphery of said flame tube; and said tubular conduit means comprises a plurality of tubular conduits each extending individually from said second annular chamber into individual communication with one opening of said plurality of openings.
 8. A combustor according to claim 3 wherein said air inlet means is adapted to introduce a swirling stream of air into the upstream end portion of said flame tube.
 9. A combustor according to claim 8 wherein said fuel inlet means is adapted to introduce a stream of said fuel axially of said swirling stream of air.
 10. A combustor according to claim 8 wherein said fuel inlet means is adapted to introduce a stream of said fuel in a direction which is from tangential to less than perpendicular to, but non-parallel to, said swirling stream of air.
 11. A combustor according to claim 10 wherein said fuel inlet means is adapted to introduce said fuel in a direction which is intermediate tangential and perpendicular to the periphery of said stream of air.
 12. A combustor according to claim 8, comprising, in further combination, means positioned downstream from said air inlet means and said fuel inlet means for causing uniform and graduated expansion of said air and said fuel during entry thereof into said flame tube.
 13. A combustor according to claim 3 wherein said air inlet means comprises: a swirl chamber disposed at the upstream end of said flame tube, and having a diameter less than the diameter of said flame tube; and conduit means for introducing a swirling mass of air into the upstream end portion of said swirl tube.
 14. A combustor comprising, in combination: an outer casing; a flame tube disposed concentrically within said casing and spaced apart therefrom to form a first annular chamber between said flame tube and said casing; a first air inlet means for introducing a first stream of air into the upstream end portion of said flame tube; a fuel inlet means for introducing fuel into the upstream end portion of said flame tube; an imperforate sleeve surrounding an upstream portion of said flame tube and spaced apart therefrom to longitudinally enclose an upstream portion of said first annular chamber and define a second annular chamber between said sleeve and said outer casing; a wall member closing the downstream end of said second annular chamber; at least one opening provided in the wall of said flame tube at a first station located intermediate the upstream and downstream ends thereof; conduit means extending from said second annular chamber into communication with said opening located at said first station for admitting a second stream of air from said second annular chamber into the interior of said flame tube; and at least one other opening provided in the wall of said flame tube at a second station located downstream from said first station for admitting a third stream of air from said first annular chamber into the interior of said flame tube.
 15. A combustor according to claim 14 wherein heat exchange fins are mounted on the outer wall surface of said flame tube, in the region surrounded by said sleeve, and extend into the portion of said first annular chamber enclosed by said sleeve.
 16. A combustor according to claim 14 wherein: a dome member is mounted in the upstream end of said flame tube; and said air inlet means comprises a generally cylindrical swirl chamber formed in said dome member, the downstream end of said swirl chamber being in open communication with thE upstream end portion of said flame tube, and conduit means for introducing a stream of air into said swirl chamber tangentially with respect to the inner wall thereof.
 17. A combustor according to claim 16 wherein said fuel inlet means comprises conduit means for introducing said fuel into the upstream end of said swirl chamber and axially with respect to said swirling stream of air.
 18. A combustor according to claim 17 wherein the downstream end portion of said dome member comprises an expansion passageway which flares outwardly from the downstream end of said swirl chamber to the inner wall of said flame tube.
 19. A combustor according to claim 16 wherein: the downstream end portion of said dome member comprises an expansion passageway which flares outwardly from a point adjacent the downstream end of said swirl chamber to the inner wall of said flame tube.
 20. A combustor according to claim 19 wherein said dome member comprises: an upstream element having said swirl chamber formed therein; a downstream element having said expansion passageway formed therein; an inner wall of said downstream element being spaced apart from and complementary in shape to the downstream end wall of said upstream element so as to form a fuel passageway between said inner wall of said downstream element and the downstream end wall of said upstream element; and wherein said fuel passageway communicates with and forms a part of said fuel inlet means.
 21. A combustor according to claim 16 wherein said fuel inlet means comprises a plurality of fuel conduits extending tangentially through the downstream end portion of said dome member adjacent the downstream end of said swirl chamber.
 22. A combustor according to claim 21 wherein: said air inlet means comprises a plurality of air conduits extending into said swirl chamber adjacent the upstream end portion thereof and tangentially with respect to the inner wall thereof; a recess is formed in the downstream end of said closure member; and said fuel conduits extend into said recess tangentially with respect to the wall thereof.
 23. A combustor according to claim 22 wherein said air conduits extend tangentially into said swirl chamber in one of a clockwise manner and a counterclockwise manner, and said fuel conduits extend tangentially into said recess in the other of said clockwise and said counterclockwise manner.
 24. A method for burning a fuel in a combustor, which method comprises: establishing separate streams of air as a first stream of air, a second stream of air, and a third stream of air; introducing said first stream of air initially into a swirl zone at the upstream end of a primary combustion zone of said combustor; exiting said first stream of air from said swirl zone into said primary combustion zone as a swirling stream of air; introducing a fuel into the upstream end of said swirl zone axially of said swirling stream of air so as to effect controlled mixing of said fuel and said air at the interface therebetween; expanding said swirling stream of air and said fuel in a uniform and graduated manner, during at least a portion of said mixing thereof, from the volume in the region of the initial contact therebetween to the volume of said primary combustion zone; burning said fuel; introducing said second stream of air, maintained separate from said first stream of air, into a secondary combustion zone of said combustor located downstream from said primary combustion zone; flowing said third stream of air, maintained separate from said first and second streams of air, in a downstream direction over and in heat exchange with an outer wall of said primary combustion zone so as to remove heat from the interior of said primary combustion zone and heat said air; and introducing said thus heated third stream of air into a third zone of said combustor located downstream from said secondary zone.
 25. A method for burning a fuel in a comBustor, which method comprises: establishing separate streams of air as a first stream of air, a second stream of air, and a third stream of air; introducing said first stream of air initially into a swirl zone at the upstream end of a primary combustion zone of said combustor; exiting said first stream of air from said swirl zone into said primary combustion zone as a swirling stream of air; introducing a fuel as an annular stratum of fuel around said swirling stream of air exiting from said swirl zone and in a direction which is from tangential to less than perpendicular, but non-parallel, to the periphery of said swirling stream of air so as to effect controlled mixing of said fuel and said air at the interface therebetween; expanding said swirling stream of air and said fuel during at least a portion of said mixing thereof, with said expansion being initiated immediately after the initial contact between said air and said fuel; burning said fuel; introducing said second stream of air, maintained separate from said first stream of air, into a secondary combustion zone of said combustor located downstream from said primary combustion zone; flowing said third stream of air, maintained separate from said first and second streams of air, in a downstream direction over and in heat exchange with an outer wall of said primary combustion zone so as to remove heat from the interior of said primary combustion zone and heat said air; and introducing said thus heated third stream of air into a third zone of said combustor located downstream from said secondary zone.
 26. A method according to claim 25 wherein: said initial contact between said fuel and said swirling stream of air occurs upon the exit of said air from said swirl zone; and said expansion of said fuel and said air occurs in a uniform and graduated manner from the volume thereof in the region of said initial contact to the volume of said primary combustion zone.
 27. A method according to claim 25 wherein said fuel is introduced tangentially to said swirling stream of air.
 28. A method according to claim 27 wherein said swirling stream of air upon exiting from said swirl zone is swirling in a direction which is one of clockwise and counterclockwise, and said fuel is introduced in a direction which is one of clockwise and counterclockwise and which is opposite to the direction of rotation of said swirling stream of air. 